Ford unveiled the Boss 429 in 1969 after NASCAR had disallowed its 427 single overhead cam motor. Decision makers inside Ford were tired of getting whupped in NASCAR competition by Chevrolet's canted-valve big-block and Dodge's vaunted Hemi, so after the SOHC motor was rejected, they scrapped the aging 427 block design altogether and produced a new, lighter, thin-wall block with a 4.36-inch bore and 3.59-inch stroke based on the 429/460 engine. And thus one of the most outlandish engines Ford ever built was born: The Boss 429.

The other version of the Boss motor, the 302, was quite successful as a road racer, and while the 429 also found its way into drag racing, its reason for existing was to dominate the oval tracks of NASCAR. To make the Boss 429 legal for NASCAR competition, Ford had to homologate the engine into at least 500 street cars every year. For that honor Ford chose the Mustang, even though the Mustang never raced in NASCAR's then-named Grand National Series. The cars themselves were produced in very limited numbers and handbuilt out of the Kar-Kraft shops in Michigan. Only 859 Boss Mustangs were produced in 1969, and in 1970 that number shrunk to 500. No Boss 429 vehicles were produced after that because NASCAR killed off all hemi-style engines with restrictive carburetor rules for the '71 season, and if Ford couldn't race the engine, it had no desire to sell it to the public.

So when Ray Wilson came across a set of Boss 429 heads-complete with the rocker arms and an appropriate intake-in a friend's shop, he jumped at the chance to buy them. There was no block to be found, and both heads were so severely damaged that if they had come off of any other motor they would have been thrown away. But with less than 1,400 Boss 429 cars ever built, Wilson knew that this trash was treasure. He paid $400 for the lot of it and hauled it to KT Engine Development in Concord, North Carolina. KT Engines is known for building winning engines for stock car racers on almost every level, but the shop recently began taking in more work from hot rodders looking for high-end engines to set their cars apart.

Wilson asked KT's owner Ken Troutman to find a way to turn what little he had into a Boss motor and went back to his own shop to begin work on a Mustang fastback he planned to turn into an appropriate Boss clone.

Block IssuesEven with his racing connections, owner Ken Troutman quickly realized there was no way to find a Boss 429 block to go with the heads. Instead, he decided the best course of action was to go with a 460 truck block as the foundation for the build even though that block and head combination were never meant to go together.

The 429/460 blocks share the same bore centers and bolt patterns as the Boss 429 block. There is really just one difference-but it's a big one. The rocker arms and springs on 429/460 blocks are oiled through lifters and pushrods. In the Boss block the oil is delivered to the heads through an oil gallery, and two galleries in the heads carry the oil to the rockers where they are oiled through the pedestals. Since there are no oil gallery holes in the deck of the 429/460 block, this creates a problem.

Otherwise, everything else inside the block is quite straightforward. Troutman used a 429 crank to de-stroke the engine to 3.59 inches and kept the stock 4.36-inch bore to hit the magic 429ci number. The rods are stock but bushed to accept a 0.990 wristpin. This allows the use of standard-sized big-block Chevy pins. The pins float inside custom JE pistons designed to get the compression ratio down to a pump-gas manageable 9.0:1. Troutman says no tricks were done with the rotating assembly because he wanted to keep the distinctive feel of the Boss 429 as true as possible.

Clinder Heads The massive cylinder heads-known as "semi-hemis" because of the significant squish areas on either side of the valves cut in on the hemispherical chamber-were practically junk but also the prize of the entire engine. By far the most manhours involved in this project were devoted to bringing the heads back to life. Troutman says he put over two pounds of filler rod into the heads. One head required significant portions of two of the combustion chambers and one of the spark-plug tunnels to be completely rebuilt. And despite the fact that these were Ford's race heads, the casting quality was surprisingly poor and impurities in the aluminum make welding on them difficult. Troutman says nearly two weeks were spent welding up damage, machining the heads back into form, pressure testing for leaks, and starting over again.

There are several clues hidden in the cylinder heads that lead us to believe that these were NASCAR race heads and have never been in a Mustang. When Wilson purchased the heads, the seller threw in a box of N.O.S. valves, which measure 2.400 for the intake and 1.900 for the exhaust. On a stock Boss 429, the intake-valve size is 2.28 inches. The heads were already machined and ported to fit the larger intake valves, which tells us there had already been massage work done here. Second, not only were the intake valves larger, but the ports had received some top-rate port work. Finally, the deck of the heads and engine block on the race engines were grooved to accept O-rings, and despite the damage these heads showed signs that this had been done. We haven't been able to trace the original use of these heads since they changed hands a few times before Wilson finally claimed ownership, but if they are former NASCAR heads they almost certainly came out of the Holman-Moody race shops in Charlotte, North Carolina, which was Ford's unofficial technology center when it came to stock car racing back then. In 1969 and 1970 when the Boss 429 was legal in competition, Holman-Moody's driver was the one and only David Pearson, and Robert Yates was porting heads in the shop. If these are indeed NASCAR heads, we bet there is a lot of history here.

Camshaft and ValvetrainTroutman went with a custom-grind camshaft from Comp Cams designed to match the new combination. The goal was to not only keep the power and torque of the original engine, but also make it manageable at parking-lot speeds. Although they are a bit of a pain to maintain, flat-tappet solid lifters were retained in a nod to the car's heritage.

Total valve lift with the new cam is 0.600 on the intake and 0.610 on the exhaust. For comparison, on the '70 edition of the Boss 429, valve lift was |0.478 intake and 0.505 exhaust. Duration at 0.050-inch tappet lift is 244 and 252 degrees, respectively, and separation is 110 degrees. To keep the gigantic valves under control, Isky springs were installed to provide 150 pounds on the seat and 410 over the nose.

OilingGetting oil to the rockers required a little ingenuity given that the oiling systems between the standard 460 block and Boss 429 cylinder heads don't match up. Troutman solved that problem with some creative plumbing. By drilling and tapping into a boss in the lifter valley, he was able to access pressurized oil from the lifter galleries. He carefully routed that oil through steel-braided lines to avoid contact with the pushrods and connected them to fittings drilled and tapped into one of the two oil galleries that run across the width of the heads. The gallery opening in the cylinder heads were no problem since they simply dead-headed into the head gasket and sealed up when the heads were torqued into place.

The galleries in the cylinder heads route oil to the bottom of the rocker pedestals where the oil travels up and feeds the rocker shaft. Holes inside the rocker spray a mist of oil on the spring on one side and the lifter cup on the other. When these heads were new, the two galleries were connected so only one inlet was needed, but while repairing the cylinder heads Troutman was forced to weld one section of the lower gallery closed. To get around this, he drilled and tapped external crossover lines at the back of both heads. Oil also drains from the heads through an external line that connects back to the oil pan. According to Troutman, the trickiest part of this setup was getting all the fittings and lines to fit underneath the stock dual-plane manifold.

Only 500 HP?On KT's engine dyno, the Boss-9 made 492 hp at 6,200 and it was still climbing when they shut it off. You're probably asking, "After all that work, why is it so weak?" There are several reasons. For one, Wilson didn't want a temperamental race car, so he asked Troutman to keep it reasonable. Reason two is that he had a lot of money in repairing the heads, and he didn't want to take the chance of hurting them on the dyno. And three, they only made two or three pulls just to make sure nothing leaked and the timing was close. There's certainly more there if Wilson wants to lean on it, but the real story is in the combination's rarity and what it took to revive it.